The rheological behavior and stability of Mg(OH)2 aqueous suspensions in the presence of sodium polyacrylate

Abstract

The magnesium hydroxide (Mg(OH)2) aqueous suspensions were prepared over a wide range of solid loading using sodium polyacrylate (NaPA) as the dispersant. The effects of solid loading, polyelectrolyte concentration, shear rate, temperature and ionic strength on the rheological behavior and stability of Mg(OH)2 aqueous suspensions have been investigated by means of viscosity and sedimentation measurements. The results showed that the apparent viscosity of the concentrated magnesium hydroxide suspensions decreased pronouncedly as the dispersant dosage was increased and reached a minimum as the dispersant concentration exceeded 0.6wt% (based on the dry powder weight). The fitting of shear stress-shear rate dependence curves with several models showed that the suspensions appeared to shift toward a Bingham-plastic flow from the shear thinning flow behavior as the NaPA dosage increased. This suggests that NaPA displays outstanding dispersing and stabilizing effects in the studied system, further evidenced by the sedimentation measurement. In addition, the apparent viscosity was also found to increase with the solid loading in the systems of aqueous Mg(OH)2 suspensions with 0.6wt% NaPA. A maximum solid loading (ϕm) at which the particulate suspensions changed from a fluid-like form into a solid-like form was determined from the ηr−ϕ relationship, using the Krieger-Dougherty model, to be 45vol% and 54vol% at shear rate of 10s−1 and 100s−1, respectively. Ionic strength and temperature also influenced the rheological behavior and stability significantly, such that lower temperature or higher ionic strength could increase the apparent viscosity. Lastly, a possible stabilization mechanism at various NaPA concentrations was discussed based on the adsorption behavior and adsorbed layer conformation of the dispersant on the particle surface.